We have a heartbreaking double murder. The victims two sisters both with children one of them able to call 911 and accuse her brother-in-law and ex-sheriff's deputy suffering from Lou Gehrig's disease, als before she died. Mara schiavocampo has the latest. Reporter: Police know that suspect well. That's because he used to be one of their colleagues. Now they're trying to piece together not only what happened exactly but why. Andrew Steele was a veteran's sheriff's deputy. His wife Ashley described as the love of his life but this morning officials are calling Andrew teel a murderer. Saying he shot and killed his wife and sister-in-law Friday at their home near Madison, Wisconsin. These events have shaken each and every one of us. Reporter: Police say the strongest evidence they have against Steele, a dying declaration from one of his victims. According to a newly released police affidavit, 38-year-old Casey tullisbohl called 911 Friday and reported that her brother-in-law Andy Steele had shot her in the back. When police arrived, they say they found her still alive and when asked who shot her, she replied, my brother-in-law. She later died at the hospital. Police say at the home they also found Ashley Steele, fatally shot and later discovered Andrew Steele in the laundry room with a handgun laying on the counter. Andy was an absolutely amazing loving husband. Never any indication of a problem. Reporter: Steele was arrested Friday but has not yet been charged and is now being held at the county jail. The 16-year deputy retired in June after being diagnosed with als. Also known as Lou Gehrig's disease. Ashley was his main advocate. Reporter: Ashley raised $75,000 for Andrew's medical care and posted numerous als ice bucket challenge videos on Facebook. The couple have two small children. Her sister was also a mom and a newlywed. Seemed so happy right now with their life. Reporter: A life that went tragically off course. Police say there was no history of domestic violence between the couple. Their children, thankfully, were not home at the time of the shooting and are now safe with relatives. Thanks. Dan Abrams is back. Boy, such a sad story and first of all let's talk about this testimony, the 911 call, could be a key piece of evidence but usually testimony isn't allowed if the witness can't be cross-examined. Hearsay evidence means a statement made out of court as this was where you don't have an opportunity to cross-examine the person who made the statement. In this case that would seem to apply except there's an exception to the hearsay rule called a dying declaration. Which it sounds like this is a classic example of. Which is not only does she call 911 and make the statement when the police arrive she also makes another statement implicating him so I don't think there's any question if this were to go to trial that would be admitted as an exception to the hearsay rule. How about the shooter learned he was suffering from als. How does that play into the case? It could cut either way. It could show a potential motive he had become deresponsible Depp and given up on life, et cetera, on the other hand he could use it to his advantage to engender sympathy although I don't know that would be effective. Could he claim some kind of mental incapacity. You can't say not guilty by reason of als. You would have to say not guilty by reason of insanity and not understanding the difference between right and wrong. That's not suffering from als but in the context of sentencing for example it could help meaning if there was a conviction and then there was a sentencing hearing and there was testimony as to how much he was suffering during this period, that could have an impact on a judge but not as to guilt or innocence. Okay, Dan Abrams, thanks very much.

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